The field of the invention is computer accessories and the invention relates more particularly to the problem of holding a printed circuit board in an edge connector on a mother board of a computer in spite of vibration.
Add-in cards are invariably used in computers for purposes such as holding a modem, a sound card, or other circuits. The printed circuit boards have one edge which extends below the bottom of the card and has a plurality of gold fingers on its sides. This edge with its gold fingers are pressed into the slot of an edge connector which has contacts which press against the gold fingers. One edge of the card is held down by a screw which passes through a slot in a metal tab affixed along one edge of the card. The other edge of the card, however, is typically unsupported and when a computer is shipped, it is often subjected to a great deal of vibration and the far edge of the card away from the screw can work its way out so that the electrical contacts between the gold fingers and the contacts of the edge connector may be compromised. Depending on the degree of severity of the contact compromise, it may result in a total loss of contact, meaning the add-in card jumped out of the edge connector slot; or intermittent contact, meaning that there are still some contacts between the gold fingers and the contacts of the edge connector, but the contact has been compromised to the degree that it is no longer reliable. This could cause the computer to malfunction. Failures of this nature are troublesome for diagnostic quality and repair reasons because the imperfect contact can work some of the time and fail some of the time, and is thus not easy to diagnose, or the failure to make good contact can make it difficult to pinpoint the root cause of the failure, such as a bad component, a bad circuit design, and the like.
Various approaches have been taken to try to solve this problem. One such approach is shown in U.S. Pat. No. 4,890,198. This patent shows a notched retainer which clips on the outer edge of the printed circuit board. A retainer is then trimmed to a length where it abuts the housing of the computer, thereby holding the circuit board in place.
U.S. Pat. No. 5,623,396 utilizes an elongated rod which has an adjustable hold-down fastener which is held between the rod and the top of the circuit board. A rod must be held above the circuit board in order for this device to function.
U.S. Pat. No. 5,303,793 uses a ratcheted card holder which is held to a post which is secured to the side of the edge connector. However, with most personal computers, there is no slotted clamp along the side of the edge connector. Also, the room between adjacent edge connectors often would not permit the securing of such a member.
Another approach is shown in U.S. Pat. No. 5,603,628 where a tie down strap is secured at both ends to the edge connector and tightened to hold the card in place. Once again, the edge connectors do not come with a place to hold such a tie down strap.
An expandable thermal-clamp is shown in U.S. Pat. No. 5,472,353 which clamp includes a spring. This clamp presses against the bottom edge of the card to hold it against the contacts. However, the conventional edge card does not have room for such a device.